Head may be cracked or warped or may be a leaking core plug on the engine block look very closily around the engine while the engine is filled with water with the engine running if you dont see anything then it could be the water pump leaking the seal may of failed look under the timing belt area with car on ramps or raised on a kerb use a torch with engine running if you see any leaks then you may have to replace the water pump or gasket and re-time the engine.
noel
September 2009